Diffusion modeling as a tool for constraining timescales of evolution of metamorphic rocks

The widespread discoveries of ultrahigh pressure rocks on the surface of the earth have considerably revised our view of rates of tectonic processes. Suitable tools are necessary to quantify the rapid rates involved in the production and preservation of ultrahigh pressure metamorphic features. It is shown here that diffusion modeling is a powerful and versatile tool for attaining this goal. The basic steps involved in the modeling process are outlined followed by a discussion of the considerable list of advantages. Major shortcomings are in the unavailability of high quality measurements of diffusion coefficients in key minerals, and in our theoretical understanding of diffusion processes in complex silicates. Two examples are provided of how recent technological and theoretical advances may contribute to overcoming these traditional hindrances, and thereby help to realize the full potential of diffusion modeling. Some sources of data on diffusion coefficients are provided in the last section.